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20
154 AZERBAIJAN CHEMICAL JOURNAL № 2 2023 ISSN 2522-1841 (Online)
ISSN 0005-2531 (Print)
UDC 66.087.97
OBTAINING OF ALKALINE FROM ALUMINATE SOLUTION BY ELECTRODIALYSIS
METHOD
A.A.Haydarov1, G.LAlyshanly1, S.A.Kuliyev2, D.T.Mehmet3
1M.Nagiyev Institute of Catalysis and Inorganic Chemistry, Ministry of Science and Education
of the Republic of Azerbaijan 2Lentatek Aerospace Aviation and Technology Inc, Ankara, Turkey 3Firat University, Elazig, Turkey
Received 15.11.2022 Accepted 26.01.2023
In the study, electrodialysis of alunite mud and aluminum hydroxide washing solutions, obtained during the processing of alunite ore, has been carried out in the study. Acid and alkali extraction from the electrodialysis process, as well as the conditions for solidification of the obtained alkali and acid, has been researched. PC Cell 64004 electrodialysis device and bipolar, anion, cation exchange membranes and the processes occurring in the membranes has been used in the experiments. Studies show that during the electrodialysis of sodium sulfate solution, if it is possible to obtain a 3-4% sodium hydroxide solution in the initial experiments, the concentration of the alkali can be increased to 5% in the alkali thickening experiments. The flow rate of 1 ml/sec, current strength - 3-4 A, voltage - 4-5 V have been adopted as the optimal conditions of the experiments. During the study of the factors effect on the concentration of the products, it has been determined that the flow rate is the main factor affecting the process. So reducing the flow rate leads to an increase in the concentration of alkali and acid. The longer the sodium sulfate solution remains in the electrolysis chambers, the higher the concentration of the obtains alkali. At the same time, although increasing the current intensity and voltage allows to achieve an increase in the thickness of the products, the rise of these parameters is not considered favorable, since the increase in the current strength has a negative effect on the quality of the membranes.
Keywords: sodium sulfate, electrodialysis, bipolar membrane, alkali, acid, alunite.
doi.org/10.32737/0005-2531-2023-2-154-162 Introduction
In the project proposed by the General Aluminum Magnesium Institute, the leaching of burned alunite in open mixers by 13% NaOH solution at 75-800C was carried out for a certain period at the Ganja Clay-soil plant [1, 2]. The project authors calculated that 110,000 tons of KOH reagent were required annually to purchase 100.000 tons of aluminium oxide. KOH alkali was obtained by electrolysis of potassium chloride solutions. Thus, 190.000 tons of KCl had to be imported from Russia each year [3, 4]. It was practically impossible to store and use the 70.000 tons of chlorine gas that was expected to be released during the processing. This approach was unsuccessful in practice due to the consumption of a large amount of alkali.
Researchers propose processing of alunite ore, roasted at 520-5500C, by potassium hydroxide to address this issue [2, 3, 5]. At this
point, the sulfate ions in the alunite go into the solution in the form of potassium (sodium) sulfate salts (without obtaining potassium chloride fertilizer). At the same time, the majority of the aluminium in the ore (98%) is still present in the insoluble residue. In subsequent operations, it is speculated to re-dissolve aluminium-enriched raw materials in the alkaline solution. The high selling price and limited raw material supply - potash, used in the potash-alkali method for processing alunite, are significant drawbacks [6, 7]. E.I.Taghiyev prefers to use soda rather than potash in the initial stage of dissolution to make the procedure simpler. Nevertheless, the recycled alumina solution needs to have alkali added to it.
As an alternative method for obtaining alkali during alunite processing, electrolysis of washing solutions of alunite mud and aluminium hydroxide is considered.
The first electrodialysis procedure to
obtain acid and alkali from sodium sulfate solution was implemented in 1923 [8]. After 1993, the literature started to cover studies on this technique for producing acid and alkali from solutions of alkali metal sulfates.
In many technological processes, sodium hydroxide solution is used as a solvent. Membrane electrolysis of sodium chloride and sodium sulfate solutions are the primary techniques for obtaining NaOH. High concentration NaOH (50%) can be obtained from the electrolysis of NaCl solution. A low-concentration solution of NaOH is available in electrodialysis (ED) and bipolar membrane electrodialysis units [9-12]. Stanislaw K. and colleagues tested which type of ion exchange membranes (Fuma Tech., Du Pont) is effective in obtaining 1-5 M (3.74-17.34%) NaOH solutions [12]. It was found that Fuma Tech. cation exchange membrane gives better results compared to bilayer Nafion membranes. All studied cation exchange membranes show a low current yield.
In another study, the possibility of obtaining sulfuric acid and sodium hydroxide from sodium sulfate solutions processed in the electrodialysis unit with Ralex bipolar membrane has been investigated [13]. It is shown that the efficiency of bipolar membranes increases with current excess. Effectively, Ralex membranes can increase H2SO4 and NaOH concentration to 1 M (9.8%) and 2 M (7.4%), respectively. In the article, the authors investigated the factors affecting the properties of the bipolar membrane: current density, and concentration of H2SO4 and NaOH. It is shown that the efficiency of BM increases as the current density increases and the concentration of acid and alkali decreases significantly. The article provides information about a three chamber membrane electrodialysis device (Figure 1).
The American patent provides information on the production of NaOH and H2SO4 from acidified sodium sulfate solutions by electrochemical method [11]. The process is carried out in a device with anode and cathode sections. As a result of electrolysis, the aqueous solution of sodium sulfate supplied to
the anode camera is decomposed into sulfuric acid and oxygen and the sodium sulfate solution supplied to the cathode area is decomposed into sodium hydroxide and hydrogen gas.
+ - + +
Fig. 1. Electrodialysis scheme of Na2SO4 solution.
In order to obtain an alkali, OH- ions must be present in the solution, and H+ ions must be present in the solution to obtain an acid. Splitting of water into ions is possible by preparing modified cation and anion exchange layered membranes on the same carrier. This type of membrane is called a bipolar membrane. Because the medium is neutral, water splitting can occur at a lower voltage, about 0.82 V.
Niftaliyev S.I. and others had conducted research on the extraction of acid and alkali from solid sodium sulfate solutions by the elec-trodialysis method, which meets the modern eco-friendly production [15]. The results of continuous experiments in a three-chamber bipolar membrane electrodialysis device showed that the device used reduces energy consumption. The authors used 0.5 mol/l Na2SO^ 0.005 mol/l H2SO4 and 0.01 mol/l NaOH solutions as model solutions. The electrodialysis device was operated with a current density of 15 mA/cm2.
Czech researchers Jan Kroupa [16] with their collaborators researched the extraction of maximally concentrated alkali and acid from sodium sulfate-containing waste water of uranium production. The authors studied factors such as voltage, current density, temperature, and solution flow rate that affect energy consumption during electrodialysis. It was found that the concentration of acid and alkali is twice as high in a three-compartment electrodialysis unit compared to a two-com-
partment system. Optimal productivity was observed at the lowest temperature - 17.20C. When the linear speed of the solution is 5 l/min, the concentration of the acid is 4.44%, and the concentration of the alkali is 4.0%. It was determined that increasing the concentration of acid increases energy consumption.
Polish researchers [17] conducted research on obtaining solutions with an alkali density of 13.96% and an acid density of 10.15% in multi-chamber devices from a sodium sulfate solution with an initial density of 80.9 g/dm3 (7.57%) in a continuous electrodialysis unit. It is indicated that the temperature inside the electrodialyzer should not exceed 600C. Therefore, electrodialysis of Na2SO4 should be carried out in a multi-stage system with inter-system cooling devices.
According to our theoretical calculations, in the method that corresponds to the principles of green chemistry, 579.6 kg of alkali are needed to leaching 1 ton of alunite by 10% NaOH solution, and 355 kg of sulfuric acid (if alunite is processed by 10% alkali) is needed to neutralize the aluminate solutions obtained.
In order to prevent external extraction of the alkali used during the research, the conditions for the extraction of alkali from the solutions obtained from the washing of aluminum hydroxide precipitate and alunite mud by the electrodialysis method were investigated.
Experimental part
Characterization of used membranes and electrodialysis devices.
Cation exchange, anion exchange and bipolar heterogeneous membranes used in electrodialysis experiments were purchased from Lianing Yinchen Membrane Technology Co LTD. Their main characteristics are given in Table 1.
The experiments were carried out in model solutions of sodium sulfate with a concentration of 35 g/l and in aluminate solutions. These solutions is containing about 3.55 g/l Na2SO4 and 0.305 g/l K2SO4.
All chemicals used in the study are analytically pure substances.
The concentration of acid and alkali formed as a result of electrodialysis was determined by titration with 0.1 M NaOH and 0.1 N HCl solutions, respectively.
C
(NaOH)
Y
(NaOH) - CH2S<VVH2SO4 (1)
Ю, % =
Cn-e 10p
(2)
Electrodialysis is the process of transporting (transferring) ions in membranes under the influence of an electric field. The PC Cell 64004 electrodialysis unit (Figure 2, a) made in Germany was used in the research work.
Preliminary experiments were carried out in a custom-made electrolysis unit. Cathode and anode plates with an area of 200 cm2 were used. Stainless steel was used as the cathode, and lead plates that were resistant to corrosion were used as the anode. Lead, which is resistant to corrosion in this medium, was used as the anode, and its area is equal to the area in the cathode chamber. The distance between the electrodes is 8 cm. Cathode and anode areas are separated from each other by an asbestos layer. The constant voltage between the electrodes can be changed in the range of 0-12 V. When the flow rate of sodium (potassium) sulfate solutions in the device's chambers is 0.25 l/min, the observed optimal voltage is 6 V and the current passing through the system is 3 A.
If the medium of the K2SO4 (Na2SO4) solution entering the chambers is neutral, if the pH of the solution in the cathode chamber reaches 12-13, and the pH of the acid in the anode chamber reaches 2-2.5, it is possible to select the necessary flow rate in the chambers and the appropriate voltage on the electrodes.
The manual of the PC Cell 64004 electrodialysis device states that this developed device can provide preliminary data for planning pilot processes.
Characteristics of the device: the minimum effective area of the membrane - 0.012 m2, the maximum effective area of the membrane -0.25 m2, the distance between the membranes is 0.5 mm, the size of the membranes is 110x110 mm. The active area of the membrane in the device is 64 cm2, it allows to process 2-5 l of laboratory solution in the chambers. Desalting and re-condensation of salt solutions can be carried out in the device.
The working principle of the bipolar membrane electrodialysis device is given in Figure 3, b. The decomposition reaction of sodium sulfate to alkali and acid is as follows [18]:
Table 1. Main characteristics of ion exchange membranes used in the process
Membranes Cation Exchange Anion Exchange Bipolar
Functions Strong acid - sulfo group Strong alkali - amino group Sulfo and amino group
Thickness (x10-3 mm) 0.17 0.30 0.19
Resistance (œxsm2) 2.45 4.24
Ionic volume capacity (mmol/g) 2.2 2.11 1.78 (cation) 0.05 (anion)
Water absorption, % 47.7 33.1 96.4
Fig. 2. PC Cell 64004 electrodialysis unit (a) and mechanism (b): BPM - bipolar membrane, AEM - anionexchange membrane, CEM - cationexchange membrane.
2Na2SO4 + 6H2O=4NaOH + H2 + 2H2SO4 + O2
The sodium sulfate solution supplied to the device is passed through the cation exchange (CEM) and anion exchange (AEM) membranes. Under the influence of electric current, sodium passes through the cation exchange membrane (CEM) and is directed (transferred) to the cathode side of the device. The movement of the sodium ion is hindered by the positively charged layer of the bipolar ion. Equivalent amounts of H+ and OH- ions are formed from dissociation of water in bipolar membranes due to constant current. The processed OH- ions pass through the bipolar membrane on the left and combine with Na+ ions that have passed through CEM, forming NaOH. At the same time, the SO42- ions formed from the dissociation of sodium sulfate pass through the ADM on the right and combine with the H- ions separated from the BPM in the anode zone to form H2SO4 acid [19].
Thus, OH- ions and H2 gas are formed due to the electrochemical reduction of water in the cathode section.
2H2O+2e ^2OH" + H2 and Na+ +OH" = NaOH; E0 = -0.828 V
A similar situation occurs with the electrochemical oxidation of water inside the other bipolar membrane, the H+ ion is released and O2 gas is formed:
2H2O-4 e ^ 4H++O21 and 2H++SO42" ^ H2SO4; E0 = +1.229 V
How the values of the current and electric charge change with the change of the voltage in the sections, the thickness of the solution was investigated by the authors in [17, 20]. It was found that during measurements, the flow rate can be determined by the consumed electric current. During the studies, it is important to keep the temperature of the solution at the appropriate level. According to the manufacturers, the membranes used can work productively up to 800C, and high temperatures can cause the membranes to fail.
It is known that the amount of heat released per unit time, Coul, can be calculated by knowing the resistance (V) and the current density.
Under standard conditions, the breakdown voltage of water is equal to 2.057 V (2 V). For each additional 1 V voltage, 1 A current intensity and 1 hour duration, 162 kC of heat is released.
Fig. 3. Electrodialysis device (a) 1 - alkaline receiving vessel, 2 - acid receiving vessel, 3 and 4 - rotameter, 5 - voltmeter/ammeter, 6 - PC Cell 64004 electrodialyzer and working mechanism.
When 6 l of electrolyte flows through the anion and cation chambers for 7 hours, the flow rate of the accumulated products is equal to 0.857 l/h. The released heat of 162 kC can increase the temperature of the solution up to 18.50C.
AT =
Q
162
= 18.5°C
U • Cw 2.517 • 3.48
2.517 l/h is the sum of the speeds of solutions flowing through the cation, anion and dialysis chambers (0.857x3 = 2.571 l/h) and Cw is the heat capacity.
Thus, if we consider that the temperature inside the electrodialyzer and the temperature of the initial solutions will not exceed 230C, the decreasing of voltage in the chambers will make the process more economically efficient.
Results and discussion
Preliminary experiments were conducted by changing the flow rate of the solutions from the chambers at different values of voltage (V) and current strength (A) in order to obtain alkali and sulfuric acid from 1% sodium sulfate solution by electrodialysis. The experiments were carried out with 500 ml of 1% Na2SO4 solution, the flow rate of sodium sulfate was changed from 1 to 10 ml/min, and the obtained results are given in Table 2.
As it can be seen, the lower the flow rate of the solution or the longer the residence time in the chamber, the higher the concentration of the alkali.
A series of experiments was carried out by monitoring the change in the concentration of the alkali depending on the flow rate of the 1% NaOH solution periodically supplied to the chamber. When the flow rate of sodium hydroxide solution in the electrodialysis chamber is 1 ml/min, its concentration increases from 1% to 4.66% within 30 minutes. During this time, when the flow rate of alkali is 3 ml/min, its concentration drops to 3.2%, and when it is 5 ml/min, to 2.56% (Table 3).
During the experiments, 1% alkaline solution was added to the cathode chamber but 0.1M sulfuric acid solution to the anode chamber in order to create electrical conductivity in the electrodialysis unit. At this time, the voltage in the system varies between 10-15 V, and the current varies between 0.32.2 A. The experiments were carried out by recirculating the same solution in the electrodialysis unit.
The highest alkalinity (NaOH - 5.06%) was obtained when the voltage was 15 V and the current intensity was 2.2 A.
Table 2. Results of alkali concentation experiments as a result of electrodialysis of Na2SO4 solution (CNa2SO4= 1%, Vn„so4 = _500 ml) _
Experiments CNaOH Voltage (U); current strength (I)
hour Flow rate 1 ml/ min
11:45 0.20% 4.5 V; 4 A
12:00 3.18% 4.5 V; 3.9 A
12:25 3.70% 4.5 V; 3.7 A
hour Flow rate 3 ml/ min
12:50 0.20% 5.5 V; 4.5 A
13:05 2.44% 5.5 V; 3.7 A
13:45 2% 5.5 V; 3.5 A
Hour Flow rate 5 ml/ min
13:50 0.20% 5.5 V; 4.1 A
14:10 1.44% 5.5 V; 3.8 A
14:30 1.42% 6 V; 4.2 A
Hour Flow rate 10 ml/ min
14:25 2.50% 4.5 V; 4 A
15:25 1.64% 4.5 V; 4 A
Table 3. Experiments on thickening of sodium
hydroxide solution (V(NaOH)=500ml , C(NaOH)=1%)
Experiments CNaOH Voltage; Current strength
Hour Flow rate 1 ml/min
10:45 2.4% 5.5 V; 4.6 A
11:00 4.56% 5.5 V; 4.6 A
11.15 4.66% 5 V; 4.5 A
Hour Flow rate 3 ml/min
10:30 3.2% 4 V; 3.8 A
10:45 3.12% 4.5 V; 4.5 A
Hour Flow rate 5 ml/min
11:00 2.56% 4.5 V; 4.6 A
Hour Flow rate 3 ml/min
10:50 0.44% 4.4 V; 4.7 A
11:05 2.16% 4.4 V; 4.6 A
11:30 2.14% 4 V; 4 A
12:00 2.16% 4.5 V; 4.5 A
12:25 2.16% 4.5 V; 4.5 A
If the intensity of the current changes between 1-2.2 A, a serious increase in the concentration of the alkali is observed, at its lower values (0.3-0.5 A), no serious change in the concentration is observed and it varies between 1.24-1.56% (Figure 4).
The most important factor affecting the concentration of the alkali in the cathode
chamber and the concentration of the acid in the anode chamber is the current density.
This factor is found by the ratio of the value of the current intensity to the cross-sectional area of the electrode and its unit is A/m2. Table 4 shows the results of changes in the concentration of alkali depending on the current density in experiments conducted in a three-chamber bipolar membrane device.
I imi . mill
( lint*, mill
Fig. 4. Time dependence of the concentration of alkali obtained from electrodialysis at different values of current strength and voltage.
Table 4. Dependence of alkali density on current density _______
Current density, A/dm2 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.6
Concentration of NaOH, % 0.16 0.36 0.44 0.56 0.01 0.67 0.72 0.76 1.04
Table 5. Time dependence of the concentration of the alkali obtained in the cathode chamber
Time, min 20 40 60 80 100 120 140 160 180 200
NaOH, g/l; (J = 1A/dm2) 15.8 16 16.4 17.5 18.1 19.4 20 20.9 21.5 22
NaOH, g/l; (J= 2 A/dm2) 16.1 17.2 18.6 20.4 22.6 24.3 25.8 27.0 28.5 30
As can be seen from the table, as the current density increases, the concentration of alkali in the solution increases. However, when the experiments are carried out in a device without a bipolar membrane, the flow rate of the solution is hindered due to the intense separation of hydrogen and oxygen gases released in the chambers. In [12], it is reported that when the current density is 50-100 mA/cm2 in the bipolar membrane electrodialysis device, a higher concentration acid and alkaline solution can be obtained due to the active dissociation of water inside the bipolar membrane.
Table 5 shows the time dependence of the concentration of the alkali obtained in the cathode chamber. The experiments were carried out with the condition that the current density was 1 and 2 A/dm2 and the initial concentration of the alkali was 15 g/l. Alkali metal sulfates of the same concentration were added in the cathode and anode chambers.
It can be seen from the table that the concentration of the alkali obtained from electrodialysis during the same time increases as time and current density increase. As a result of electrodialysis of Na2SO4 solution with concentration of 2% (U=10 V, I=1 A), the dynamics of obtaining an alkaline solution with concentration of 5.6% in the cathode chamber is given in Figure 5.
It can be seen from the picture that if the concentration of the alkali entering the chamber is
u
1 -
0 —'-1—'—i—'—i—'—:—--i-1—1—--1—■—[—1—[—--1
0 2 0 40 SO 63 100 120 MO 160 ISO 200
time, mm
Fig. 5. Time dependence of alkali concentration.
1.8%, the concentration of the solution leaving the chamber reaches 5.6% within 3 hours. To increase the concentration of acid and alkali, it is necessary to reduce the flow rate of the solution. Increasing the duration of electrodialysis rises the concentration of both acid and alkali.
In Figure 6, the change of the concentration of alkali in the cathode chamber and the concentration of acid in the anode chamber was monitored for 6 hours at the same time. In the solutions added to the periodic chambers, the concentration of the acid is 2 times higher than the concentration of the alkali. During the electrolysis of sodium sulfate, hydrogen and oxygen gases are released in chambers other than alkaline and acid. The change of the volume of the gas collected in the receiving vessel as a function of time is given in Figure 7.
9:45 9:55 10:25 10:30 11:15 11:45 12:45 13:45 14:45 15:45
time
Fig. 6. Time dependence of the change in concentration of alkali in the cathode chamber and acid in the anode chamber (C= 2.5%, I1 = 1 A, I2 = 2 A, flow rate, 1 and 5 ml/min, U1 = 15 V, U2 = 30 V, respectively).
time, min
Fig. 7. Variation of the volume of gas collected in the receiving vessel as a function of time.
Conclusion
By using bipolar, anion and cation exchange membranes, during the electrodialysis of sodium sulfate solution in the PC Cell unit made in Germany, in the initial experiments 34% sodium hydroxide solution is obtained. It is also possible to increase the concentration of the alkali to 5% in the alkali thickening experiments.The flow rate of 1 ml/sec, current strength - 3-4 A, voltage - 4-5 V are accepted as the optimal conditions of the experiments. The results obtained during the studies in the flow rate range of 1-10 ml/min showed that the lower the flow rate, the longer the solution stays in the chambers, which leads to an increase in the concentration of alkali and acid. The alkali and acid obtained as a result of electrodialysis can be applied to alunite processing technology.
Acknowledgements
The authors express their gratitude to the Center of shared analytical instruments and equipment, Institute of Geology and Geophysics for providing the laboratory facilities.
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QOLOViNiN ELEKTRODiALiZ METODU iLO ALUMiNAT MOHLULUNDAN ALINMASI
A.O.Heyd3rov, G.LAh$anh, S.A.Quliyev, D.T.Mehmet
Tadqiqat ijinda alunit filizinin emali zamani alinan alunit ¡laminin va aluminium hidroksidin yuma mahlullarinin elektrodializi aparilmi§dir. Elektrodializ prosesindan turjju va qalavi alinmasi, alinan qalavi va turjjunun qatilajmasi ¡jaraiti tadqiq edilmijjdir. Tacrubalarda PCCell 64004 elektrodializ qurgusu va bipolyar, anion, kation dayi§dirici membranlardan istifada edilmijj va membranlarda ba§ veran proseslar ara§dirilmi§dir. Tadqiqatlar onu gostarir ki, natrium sulfat mahlulunun elektrodializi zamam ilkin tacrubalarda 3-4%-li natrium hidroksid mahlulu almaq mumkundursa, qalavinin qatilajjdirilmasi tacrubalarinda qalavinin qatiligini 5%-a kimi artirmaq olur. Tacrubalarin optimal ¡jaraiti olaraq axin surati 1 ml/san, carayan ¡jiddati - 3-4 A, garginlik - 4-5 V qabul edilmijjdir. Mahsullarin qatiligina tasir edan amillarin tadqiqi zamam muayyanlajdirilmijdir ki, axin surati prosesa tasir edan asas faktor olub, axin suratinin azaldilmasi qalavi va turjunun qatiliginin artmasina sabab olur. Natrium sulfat mahlulunun elektroliz kameralarinda qalma muddati na qadar goxdursa alinan qalavinin da qatiligi gox olur. Bununla yanaji carayan ¡jiddatinin va garginliyin artinlmasi mahsullarin qatiligimn artmasina nail olmaga imkan versa da, carayamn gucunun artmasi membranlann keyfiyyatina manfi tasir etdiyindan bu parametrlarin artimi alverijli hesab olunmur.
Agar sozlzr: natrium sulfat, elektrodializ, bipolyar membran, qalavi, tur§u, alunit.
ПОЛУЧЕНИЕ ЩЕЛОЧИ ИЗ РАСТВОРА АЛЮМИНАТА МЕТОДОМ ЭЛЕКТРОДИАЛИЗА
А.А.Гейдаров, Г.И.Алышанлы, С.А.Кулиев, Д.Т.Мехмет
В исследовании проведен электродиализ алунитового шлама и промывных растворов гидроксида алюминия, полученных при переработке алунитовой руды. Исследовано извлечение кислоты и щелочи из процесса электродиализа, а также условия отверждения полученных щелочи и кислоты. В экспериментах использовали электродиализный аппарат PC Cell 64004 и биполярные, анионообменные, катионообменные мембраны и процессы, происходящие в мембранах. Исследования показывают, что при электродиализе раствора сульфата натрия, если в начальных опытах удается получить 3-4%-ный раствор едкого натра, то в опытах по сгущению щелочи можно довести концентрацию щелочи до 5%. За оптимальные условия экспериментов приняты скорость потока 1 мл/сек, сила тока 3-4 А, напряжение 4-5 В. При изучении влияния факторов на концентрацию продуктов установлено, что скорость потока является основным фактором, влияющим на процесс. Так уменьшение расхода приводит к увеличению концентрации щелочи и кислоты. Чем дольше раствор сульфата натрия остается в камерах электролиза, тем выше концентрация получаемой щелочи. В то же время, хотя увеличение силы тока и напряжения позволяет добиться увеличения толщины изделий, повышение этих параметров не считается благоприятным, так как увеличение силы тока отрицательно сказывается на качестве изготовления. мембраны.
Ключевые слова: сульфат натрия, электродиализ, биполярная мембрана, щелочь, кислота, алунит.
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